This invention relates to injection molding and more particularly to an injection molding system having reduced heat loss from a heated nozzle to the surrounding cooled mold.
In this type of system, the heated nozzle is securely seated in a well in the cooled mold. As shown for instance, in the applicant's U.S. Pat. No. 4,557,685 entitled "Heated Nozzle for Injection Molding Apparatus" which issued Dec. 10, 1985, the nozzle has an insulation bushing which seats against a shoulder to locate the nozzle with an insulative air space between it and the surrounding mold. As is well known, it is critical to the successful operation of the system that the temperature of the melt be maintained within a predetermined narrow temperature range as it flows through the heated nozzle. However, it has been found that previous nozzles of this type suffer greater temperature drop at their ends than in the middle which makes a uniform temperature difficult to achieve. One attempt to deal with this problem is to increase the pitch of the helical heating element in the middle as shown, for instance, in the applicant's Canadian patent application Ser. No. 549,519 filed Oct. 16, 1987 entitled "Injection Molding Nozzle with Resilient Sealing and Locating Flange".
Canadian application Ser. No. 549,519 relates to a nozzle having a circumferential sealing and locating flange which extends across the insulative air space and abuts against the surrounding inner surface of the well in the cooled mold. As will be appreciated, this necessarily results in heat loss from the heated nozzle to the cooled mold. The applicant's Canadian patent application Ser. No. 557,681 filed Jan. 29, 1988 entitled "Improved Mounting for Injection Molding Nozzle" discloses reducing this problem by machining a circumferential groove in the cavity plate to form a thin wall portion against which the sealing and locating flange abuts. While this arrangement is a substantial improvement, it has the disadvantage of being relatively difficult to machine and still results in considerable heat loss from the nozzle.